Jeep Straight Six Stroker Build: Big Power on a Budget

The Jeep straight six is one of the greatest engines of all time. But that doesn’t mean it can’t be improved. Newcomer Racing shows us how to put together a big power, naturally aspirated stroker 4.0 Jeep engine without spending big coin. The basic recipe is to use the block and connecting rods from a 4.0 Jeep with the longer stroke crank from a 4.2. Of course, there’s a lot more too it than that, and we’ll spell it out there.

Also, don’t forget to scroll down to the end of this post. Newcomer recently followed up with pics of the engine installed in a Cherokee and even results of a tuning session on a chassis dyno.

And if you want to get one of your own, check out

Although not complete, here’s a partial parts list. (Note: For the stock replacement components they may not be the exact same brand Newcomer Racing uses.):

Sealed Power pistons

Hydraulic lifters

Valve Springs

Stamped Steel Rocker Arm Kit

Jeep 4.0 block
The newer NVH “Noise Vibration and Harshness” blocks seem to work best because they are a beefier casting and use a crank girdle.
Sealed Pro Pistons
Sealed Pro pistons dropped into the block.
Jeep 4.0 Stroker Crankshaft
The crank is from a 4.2 liter Jeep engine. The 4.2 has a longer 3.895 inch stroke versus the 4.0’s 3.414.
Jeep NVH block stud girdle
The NVH block from newer Jeeps uses a stud girdle for extra strength. For a stroker build you may need to add washers to create a little more space for the extra stroke.
Jeep connecting rods Sealed Power pistons
Sealed Power pistons go onto the stock connecting rods.
Jeep 4.0 Bullet Racing Cam
The cam is a hydraulic flat tappet from Bullet Racing Cams.
Jeep 4.0 Cylinder Heads
The head we will be using is a stock cast iron unit with some port work done to help flow.
Jeep 4.0 engine build
Stock valve springs will control the valves.
Jeep 4.0 intake manifold
The intake and exhaust flow off the same side of the cylinder head.
Jeep stroker 4.0 on the dyno
On the engine dyno.
Jeep stroker 4.0 dyno results
Dyno results.
Jeep stroker engine
The stroker engine back into its home in the Cherokee.
Jeep Cherokee
Jeep Chassis Dyno Results
Dyno results with a little tuning using the stock efi and fuel injection once the engine is in the Cherokee.

13 Responses

  1. How much for the 4.0 striker? Where is your pricing??
    • jeff
      This build complete from intake to oil pan is right around $5,000 right now from Newcomer Racing. But every build is different. You can reach them at Thanks
  2. Please do something for those of us saddled with AMC 2.5l I4. Come on and help fan out!!!! Something to get us super excited! Okay we challenge you to put together a 250 horse 2.5!!!!!!!!!!! From a fan in need of power!!!!!!!!LOL Ray Kilsby
  3. I Worked for AMC/JEEP/ CHRYSLER engineering from 1976 to 2001, now retired. I was Engr in charge of airflow development. I'm the person that developed the 4cylinder JEEP & The JEEP 4.0L Cyl heads. (This is not a joke!) Back in 1993 I developed a 4.0L JEEP engine for drag racing, NHRA Competition Eliminator. It was an E/EA for Garth Hill and Charlie Williams. Set National record in 1996 at 8.60ET/ best speed 150.90 MPH, very quick & fast. Runner Up at the 1995 U.S.Nationals (INDY), Foul start (should have won). Currently helping Bob Salemi from Rhode Island, he runs a stocker 92 Jeep Comanche in NHRA STOCK CLASS, R/SA. Set Record at 12.95, runs off a 14.05 index, #1 qualifier Epping NH 2014, 12.879 ET/ 100.8 MPH, Best ET 2019 12.792/ 102.44 MPH, worked on valve train Harmonics, found more power. BEST stock cast head from production is either 1992 or 93 castings, New Haven foundry look for NH cast on top between rocker pedestals. Small Exh port heads no good for power, Made for emmisions, Faster CAT light off time so PRE-CATS not necessary (Cost factor). Just want to let you know if I can help you on anything related to 4 cyl or 4.0L Jeeps let me know. I also do Engine Computer modeling, engine combination, cam selection, intake manifold tuning, header tuning, etc. All variables investigated. Nice job! I enjoy your DYNO testing on the 4.0L stroker project. Later, Rick
    • jeff
      Very cool. Thanks!
      • I won't drop anymore comments after this, promise! There are still two YouTube video's showing our E/EA comp elim 32 bataam Altered. One from 1995 U.S. Nationals at INDY Final Round. The other from SPRING NATIONS, Columbus, Ohio 1997. Titled: 1995 NHRA U.S. NATIONALS AT INDIANAPOLIS RACEWAY PARK (have to go to time 1:48:18) 2nd Video was a middle round from the Spring Nationals at Columbus, Ohio in 1997. Both cars run same class E/EA , Yellow car was Jerry Arnold having a FORD inline 6cyl 250in3, Garth Hill drives our 4.0L 248in3 Jeep, both engines have 3 500cfm two barrels, & Automatics. Titled: NHRA COMPETITION ELIMINATOR PPV (Time: the second pair of cars to run, right after John Lingenfelter's OLDS dragster) Hope you like the video's! NO more e-mails!
    • Rick, I love reading comments , seem to always learn something new. Especially when "Facts" come from someone that knows first hand , such as yourself. How many of those NH heads were made? Any chance a guy in California might ever stumble across one at the local parts yard? Again great to hear the stories, great videos !! Congrats on the success. A million thanks for your work on one of the best motors ever made. (In terms of reliability and longevity) You sir are a pioneer and will always be remembered for your contributions. (Best thing that ever happened to the 4.0 was the change in airflow thru the head). Sure would love to hear more of your stories. Would buy your book if you wrote one.
      • Hi Cody! I haven't looked at this website until now? Explains why I didn't respond to your questions? The best 4.0L production iron cylinder head is a 1992 casting NH. The 92 and NH are cast on top of the casting under the valve cover, can't miss it! You can find these 4.0L heads in any junk yard or an entire engine. Using a small tootsie roll in a grinder you can touch-up the short side Intake and exhaust port radius (just blend the machining around the corner to form a nice radius. This one simple operation will increase airflow, don't get carried away just a cleanup blending. The Hill & Williams Competition Eliminator JEEP 4.0L Drag head was a 92 casting using a 2.055"int valve (lite wt titanium) flowed 312 cfm at about .675" lift. Exhaust valve was a 1.550" and flowed about 240cfm at .700" using a 4" x1.75" od flow pipe. Maximum porting on Intake ports but much less port work on Exh ports.. Having a naturally aspirated engine the CR was at 13.5, small dome JE piston. 3.935" bore, 6.000" alum rod, 3.410" stroke using a 2.000" Small Block Chevy rod Journal.. Bearings easy to find. Used stock production main bearings, mains .0028" and rods .0025" clearance. Sorry? to much detail? Fingers are tired! To Bobby's Question? I did the 3.7L and 4.7L cylinder head development also. I will elaborate next time on a 4.7L flow improvement for more power. Rick..
    • Rick Mudge. That’s a name I haven’t heard in almost 20 years now. Remember the Camaro I was building when you guys used to come into Kool’s after ice skating? I still have that turd. Well oddly enough, I could use some of your expertise these days. I’m back around Detroit and still doing car stuff, and wondered if you still have that flow bench in your garage...? I’d love to bring something by and pick your brain soon if that’s still possible. I’m glad to see you’re still out there!!! If I had your number after all these years I would just call you. Hopefully you get this reply somehow...
  4. want to talk about 4.7 jeep engine.
  5. I am shopping for a motor and Auto trans to swap in my 2004 Jeep LJ 4.0. Saw your stroker motor and wanted to get more info. My existing 4.0 has 180k miles on it and just recently started tapping sound.
  6. Nice job and interesting info - I am looking for a stroker for my 1995 YJ I completely resorted over the last 3 years. I was wondering about the huge difference in horse power between motor dyno (~300 PS) and the dynojet values after motor is back in the Cherokee ( 236 PS). The peak values are at different rpm s as well. If it is rear wheel power, assuming 64 PS for drivetrain losses seems to be very high. Would appreciate your explanation - Thanks, Frank

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